The present invention relates to methods for applying a negative pressure over a suction sector of an air-pervious mantle of a rotating roll within which a suction chamber is situated which extends over the suction sector of the roll.
The invention also relates to a suction roll comprising a cylindrical air-pervious mantle and which is rotatably mounted at its ends and within the interior of which a suction chamber is situated.
Suction rolls comprising air-pervious mantles having zones subjected to negative pressure are known. Such rolls are used in apparatus for manufacturing and processing various web-like materials, such as paper, textile or plastic webs, as well as in apparatus that process sheet materials, such as printing machines or sheet cutters. Generally, such rolls are provided with perforated and/or grooved mantles through which negative pressure is applied to the web or sheet that is in contact with the suction zone of the roll.
A commonly used conventional suction roll of the type used in paper machines comprises an air-pervious mantle within which a suction box defining the suction zone is situated. The interior of the suction box is connected to suction source through the end or ends of the roll.
Such conventional suction rolls require the use of axial seals and end seals for the suction box which rub against the inner surface of the roll mantle. Consequently, these seals tend to wear during use and eventually must be replaced which is considered to be a drawback of this conventional construction. Another drawback is that the inner surface of the suction roll must be machined and ground with a high degree of precision to obtain a good sealing surface for the suction box. This increases the manufacturing costs of the roll. A suction roll provided with contact-type sealing elements also requires relatively frequent servicing which of course results in down time in the production process. The sealing water which is occasionally used in connection with suction rolls in paper machines also causes problems.